This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Biological nitrogen fixation is the dominant natural nitrogen source for biological system in the earth. Catalyzed by nitrogenase MoFe protein, it reduces dinitrogen to biologically accessible ammonia. Recently, we obtained an inactivated form of MoFe protein. Our biochemical data indicated that it undergoes significant conformational change and could be a trapped intermediate form of MoFe protein. SAXS can provide direct biophysical evidence of this shape change of the protein in solution, helping get insight of the mechanism of MoFe protein.